Fix broken seq2seq example
Fix broken seq2seq example

Reviewed By: harouwu

Differential Revision: D5423060

fbshipit-source-id: 4537b020546503a1f9cb237257ab3c42665ae07f

sf-wind/caffe2,Yangqing/caffe2,sf-wind/caffe2,Yangqing/caffe2,davinwang/caffe2,sf-wind/caffe2,sf-wind/caffe2,bwasti/caffe2,davinwang/caffe2,Yangqing/caffe2,davinwang/caffe2,xzturn/caffe2,davinwang/caffe2,pietern/caffe2,pietern/caffe2,davinwang/caffe2,xzturn/caffe2,pietern/caffe2,sf-wind/caffe2,pietern/caffe2,Yangqing/caffe2,bwasti/caffe2,caffe2/caffe2,pietern/caffe2,bwasti/caffe2,bwasti/caffe2,xzturn/caffe2,Yangqing/caffe2,xzturn/caffe2,xzturn/caffe2,bwasti/caffe2